This invention relates to new polyetherpolycarbonate diols based on 1,6-hexanediol and to processes for their production and use.
Aliphatic polycarbonate diols have long been known. They are prepared from non-vicinal diols by reaction with diarylcarbonate (DOS No. 1,915,908), dialkylcarbonate (DOS No. 2,555,805), dioxolanones (DOS 2,523,352), phosgene (DOS No. 1,595,446), bischlorocarbonic acid esters (DE-PS No. 857,948) or urea (P. Ball, H. Fuillmann and W. Heitz, Angew Chem. 92 1980, no. 9, pages 742, 743). Of the diols described in the literature, only those exclusively or largely based on 1,6-hexanediol have hitherto acquired any real technical significance. Thus, high-quality polyurethane elastomers and coating compositions are prepared from hexanediol polycarbonate by known methods. Outstanding resistance to hydrolysis makes the hexanediol polycarbonates particularly suitable for the production of articles having a long useful life. The hydrolysis resistance of such polyurethanes is known to be far better than that of polyurethanes based on adipic acid polyester as the diol component. Pure hexanediol polycarbonates (molecular weight 500 to 4000) are waxes having a softening point of 45.degree. to 55.degree. C. (according to molecular weight). As a result of the tendency towards crystallization of the soft segment, the corresponding polyurethanes tend to harden and lose their flexibility at low temperatures. To eliminate this serious disadvantage, hexanediol polycarbonates in which the softening point was lowered by incorporation of foreign components were developed. Since the relatively long chain diols suitable for this purpose were not technically available, adipic acid (DAS No. 1,964,998), caprolactone (DAS No. 1,770,245) or di-, tri- and tetraethylene glycol (DAS No. 2,221,751) were used instead. Reduction in the hydrolysis stability of the polyurethanes by the readily hydrolyzing ester groups or the hydrophilic ether segments resulted.
Another disadvantage of hexanediol polycarbonates is their relatively high intrinsic viscosity (for example, approx. 5000 mPa.s at 60.degree. C. for a molecular weight of 2000) which leads to certain processing difficulties particularly when polyurethane production is to be carried out by the two-stage process via an isocyanate prepolymer.
High-quality polyurethanes (PU) are being increasingly used in applications where they are exposed not only to hydrolytic influences but also to attack by microorganisms. This applies, for example, to rollers in printing works or textile factories, to cable sheaths, to spring elements and vibration dampers in machine construction, to coatings for awnings, flat roofs and garden furniture and to elastomeric fibers in leisure fabrics. In these fields, polyurethanes based on aliphatic polycarbonates show a susceptibility similar to that of polyurethanes based on aliphatic polyesters.
It is known that polyurethanes based on polyethers are significantly more resistant to degradation by microorganisms. The polymers of tetrahydrofuran which are the only materials contemplated and actually used for the above-mentioned applications are in turn attended by other disadvantages. For example, their crystallinity leads to a tendency of the PU to harden at low temperatures, particularly when the desired property spectrum of the PU requires the use of soft segments having average molecular weights of 2000 and higher. The resistance of the polyether based PU to swelling both in water and in organic solvents is only moderate as is their tear propagation resistance.
U.S. Pat. No. 4,463,191 describes polyether polycarbonates corresponding to the following general formula ##STR1## in which R represents --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --
n represents 7 to 45 and PA0 m represents 0 to 18, PA0 R represents an alkylene radical containing from 1 to 10 (preferably from 2 to 6) C-atoms or a cycloalkylene or arylene radical containing from 6 to 10 C-atoms, PA0 x represents a number from 2 to 6 and PA0 y represents a number from 3 to 5. PA0 R' represents an alkylene radical containing from 2 to 15 (preferably from 2 to 6) C-atoms or a cycloalkylene or arylene radical containing from 6 to 15 C-atoms and x represents an integer of from 2 to 6 may also be used. Specific examples of these diols include: 1,6-hexamethylene-bis-(.beta.-hydroxyethylurethane) and 4,4'-diphenylmethane-bis-(.beta.-hydroxybutylurethane). Diol urethanes corresponding to the general formula ##STR2## in which R" represents an alkylene radical containing from 2 to 15 (preferably from 2 to 9) C-atoms or a cycloalkylene or arylene radical containing from 6 to 15 C-atoms, PA0 R'" represents hydrogen or a methyl group and x represents the number 2 or 3 are also useful as chain terminators. Specific examples include 4,4'-diphenylmethane-bis-(.beta.-hydroxyethylurea) and the compound ##STR3## For some purposes, it is advantageous to use polyols containing sulfonate and/or phosphonate groups (DE-OS No. 2,719,372), preferably the adduct of bisulphite with 1,4-butanediol or alkoxylation products thereof.
and processes for their production and use. More specifically, these polyether polycarbonate diols are prepared by condensation of polytetramethylene ether glycols having an average molecular weight of from 500 to 3000 (preferably from 650 to 2900) with dialkylcarbonates, cyclic carbonates or phosgene. A range for the average molecular weights of the polyether carbonates of from 828 to 51,192 is derived from the general formula. The lowest value for the ratio of ether groups to carbonate groups is 12:1 and the highest value is 46.3:1. Only slight replacement of ether groups by carbonate groups occurs in the described products. Consequently, only a slight change in the property spectrum of the polyether carbonates in relation to the pure polytetramethylene ether glycols occurs.
The same also applies to the products disclosed in U.S. Pat. No. 4,476,293 where copolyether diols of tetrahydrofuran and 10 to 80 wt. % of another cyclic alken oxide containing 2 or 3 carbon atoms in the ring (epoxides and oxetanes, molecular weight 600 to 3000) are condensed as starting materials to polycarbonates for the production of polyether carbonate diols. However, such products are unsuitable for the production of high-quality polyurethanes because experience has shown that the hydrophilic ether segments and/or lateral substituents adversely affect the performance properties of the polyurethane products to a considerable extent.
Hydroxyl-terminated polyethers based on 1,6-hexanediol have also long been known. They may be prepared by direct etherification of hexanediol using acidic catalysts such as, for example, p-toluene sulfonic acid (U.S. Pat. No. 2,492,955) or benzene- or naphthalene disulfonic acid (DAS No. 1,570,540).
The condensation reaction, which takes place at temperatures of from 150.degree. to 200.degree. C., is accompanied by secondary reactions and discoloration. The higher the desired average molecular weights, the greater the extent of these secondary reactions and discoloration. Obtaining the molecular weights of 1000 to 2000 which are typical and necessary in polyurethane chemistry requires long reaction times at relatively high temperature. The secondary products oxepane, hexadiene and hexanol distill off with the water of condensation so that the yield is considerably reduced (U.S. Pat. No. 2,492,955). The products may also contain terminal double bonds instead of OH groups. These terminal double bonds act undesirably as chain terminators in the synthesis of polyurethanes (U.S. Pat. No. 2,492,955).
The hexanediol polyethers are crystalline with softening points above 60.degree. C. The polyurethanes produced from them show poor low-temperature behavior (poor low-temperature flexibility, expansion crystallization). For the reasons already mentioned, they have not hitherto acquired any technical significance.